The invention relates to a pump, a compressor or an engine, which may be endothermic, that displaces volume by means of pistons connected to the driveshaft without oscillating connecting rods. The machine may have a variable displacement.
In the field of endothermic engines, there exist several configurations in use today: engines having reciprocating pistons connected to a crankshaft with connecting rods; volumetric lobe (Wankel) engines having a rotor eccentric to a driveshaft; and engines having axial pistons, i.e. pistons parallel to the driveshaft and driven in reciprocating motion with a circular inclined cam, such that the pistons are displaced axially. The latter arrangement does not yield high performance.
In the field of pumps/engines or fluid compressors, both for compressible and incompressible fluids, several piston arrangements are known: in-line pistons, pistons mounted axially, pistons with an oscillating barrel or an oscillating plate and radially mounted pistons.
In each of the above-mentioned piston arrangements, the pistons are connected to the driveshaft with connecting rods. In the case of radially mounted or in-line pistons, the connecting rods oscillate in a plane perpendicular to the driveshaft. In the case of axially mounted pistons, the connecting rods oscillate as they run on the conoid surface of the swashplate, because the point of contact between the crank end of the connecting rod and the swashplate varies with the inclination of the swashplate, while the piston end of the connecting rod remains at the center of the cylinder.
Each of the above-mentioned mechanisms, with the exception of the endothermic lobe (Wankel) engine, have large overall dimensions. Further, none have high efficiency, and the efficiency depends on the conditions of use.
In particular, for rotary lobe (Wankel) engines, the sealing parts have a short life because they are subjected to heavy wear. This results in a loss of compression and a resulting loss of efficiency. Special materials must be used that are very expensive and difficult to obtain.
Endothermic piston engines, in all their various configurations, have a limited speed of rotation due to the alternating or oscillating motion of the pistons, connecting rods, valves and crankshaft. The crankshaft is typically difficult to manufacture. Axial thrust from the piston is transmitted to the connecting rod at varying angles, causing a reaction with the cylinder wall; this reaction causes heavy wear, requiring the use of high performance lubricating oils. In four-stroke engines, efficiency is reduced because of the restricted passageway in the valves and because it is impossible to ideally design the combustion chamber due to various design considerations.
Regarding pumps for compressible fluids, those machines suffer the same disadvantages as those encountered for endothermic piston engines. Piston pumps for compressible fluids have low efficiency due to the mechanical friction of the connecting rods, in addition to high weight, large overall dimensions and high cost.
Pumps for incompressible fluids are typically used in hydrostatic transmissions and for the pumping of other liquids. Pumps having radial or inline cylinders, while providing fairly good performance, have large overall dimensions and high manufacturing costs. Incompressible fluid pumps having axial cylinders may be subdivided into the following two categories: pumps having cylinders arranged in a barrel inclined with respect to the axis of the shaft, and pumps have an inclined plate on the shaft for guiding pistons within cylinders that are parallel to the axis of the shaft. Both arrangements unacceptably limit the speed of rotation, because of centrifugation of the crank end of the connecting rods. In addition, the arrangement having cylinders parallel to the driveshaft has very low efficiency at low speeds and may not be used in an open hydraulic circuit. The acceptance of both arrangements in the market has been further limited by high manufacturing costs.
WO-A 86/00662 discloses a piston machine in which an assembly of cylinders is arranged equidistantly about a first axis of rotation, and an assembly of corresponding pistons is arranged equidistantly around a second axis of rotation. Each piston comprises a ring member that is displaceable laterally of the piston itself to enable the ring member to move substantially rectilinearly of the corresponding cylinder while the piston itself moves through a curved path relative thereto. The second axis passes through the intersection of the circular plane formed by the spherical ring members with the first axis. While this machine eliminates many parts associated with reciprocal motion, performance is adversely affected by periodic shocks of the ring member during operation. Performance is adversely affected by those vibrations, by friction caused by centrifugation and by the thrust of the ring members toward the cylinder walls.
U.S. Pat. No. 3,910,239 discloses a piston power unit primarily for use as an internal combustion engine. The machine has a single cylinder curved about a center, intake and exhaust ports at opposite ends of the cylinder, and a pair of opposed pistons movable in the cylinder towards and away from each other in compression and power strokes. The pistons cover the ports during most of the stroke, and successively open the ports as the pistons approach ends of their respective power strokes. A pair of connecting rods connect a pair of crankshafts, including intermeshing gears, to the pistons.
This piston engine presents problems in that the thrust of the pistons toward the cylinder wall and the centrifugal force on the pistons increase the friction of the piston on the outer cylinder wall, adversely affecting performance. The design is useful only for engines having asymmetric port timing, as clearly stated in the specification. The improvements to this machine disclosed in U.S. Pat. No. 3,338,137, by the same inventor, are for structural aspects of manufacturing only.
There is a long-felt need to improve the characteristics of the above-described reciprocating volumetric machines by increasing efficiency under all conditions and reducing weight, overall dimensions and manufacturing costs. From the above, technical problems would be solved in reciprocating volumetric machines by eliminating all parts have oscillating motion, which would improve performance, while at the same time reducing overall size and weight.